The present invention relates generally to an electronic circuit unit and an electronic apparatus, and more particularly to a holding fixture that holds a component and mounts the component on a circuit substrate, an attachment method of the holding fixture to the electronic circuit board, etc. In this application, the component covers, but is not limited to, a heat sink that radiates a semiconductor device, such as a CPU, and a cooling fan that cools the same. The electronic circuit unit covers, but is not limited to, a motherboard and various extension boards. The electronic circuit unit covers, but is not limited to, the electronic circuit board mounted with the component. The electronic apparatus covers, but is not limited to, a laptop personal computer (“PC”), a personal digital assistant (“PDA”), a portable game machine, various drives, a display integrated type or slim type desktop PC, and a word processor.
The demands for electronic apparatuses typified by a PC have recently increased. In particular, along with remarkable developments and spreads of personal information apparatuses, such as a laptop PC and a PDA, these portable information apparatuses have been required to be smaller and lower-profile. In addition, as higher-performance and more multifunctional portable information apparatuses are demanded, various functions and units are installed in these apparatuses.
However, since the demands for miniaturization and low profile are not always compatible with the demands for high performance and multiple functions, the information apparatus would become larger as it possesses all the functions. In addition, since the high-performance and multiple functions would generally increase the calorific value of the information apparatus, the apparatus or its electronic components are required to efficiently radiate or cool the information apparatus as the information apparatus improves its functionality. The radiating heat sink becomes larger and heavier as the calorific value increases. It would become more important to consider the influence of radiations, vibrations and impacts by a holding fixture (or a retention mechanism) that holds the heat sink, and a reinforcing plate used to attach the holding fixture to a circuit board.
The electronic apparatus generally has an electronic circuit board mounted with plural electronic components. A semiconductor device, such as a central processing unit (“CPU”), is often mounted on the electronic circuit board. FIG. 6 is a view for explaining a conventional retention structure for a heat sink (not shown) that radiates the CPU 102 mounted on the electronic circuit board (or substrate) 101. A reinforcing plate 104 is attached on a bottom surface 101a of the substrate 101. The reinforcing plate 104 has a rectangular shape similar to a holding fixture 105, and arranges screw fixing studs 104a at four corners thereof.
The holding fixture 105 is attached on the top surface 101b at the opposite side to the reinforcing plate 104 so that the holding fixture 105 and the reinforcing plate 104 sandwich the substrate 101. The holding fixture 105 has a rectangular shape and a center hole 105a, which encloses the CPU 102 mounted on the substrate 101. The substrate 101 and the holding fixture 105 have four perforation holes 101c and 105b in place corresponding to the screw fixing studs 104a, and four screws 106 fasten the holding fixture 105, the substrate 101 and the reinforcing plate 104 to each other.
This attachment uses the reinforcing plate 104 to fix the holding fixture 105 upon the substrate 101 without fail. The holding fixture 105 has attachment holes 105c used to attach the heat sink. The heat sink contacts the CPU 102 and radiates the CPU 102 by inserting attachment fittings (not shown) into these attachment holes 105c. The attachment structure of such a holding fixture is disclosed in Japanese Utility-Model No. 3,083,951.
However, this structure results in the increased number of components and increased cost. In addition, the increased number of assembly steps spends lots of time and causes assembly task errors. If the reinforcing plate 104 is omitted in order to reduce the number of components, the holding fixture 105 should be fixed directly onto the substrate 101. The heat sink should be made heavier so as to improve the radiation efficiency. Due to the larger contact force to the CPU 102, the direct fixation of the holding fixture 105 onto the substrate may possibly damage the substrate 101.